The present invention relates to a latch needle for textile machines, comprising: a needle shank having a longitudinal slot formed therein, the needle shank comprising a needle hook located at one end of the needle shank and two opposing shank cheeks each defining a lateral side of the longitudinal slot; a latch pivotably disposed in the longitudinal slot, the latch having a bearing bore; and bearing means attached to at least one of the shank cheeks and in communication with the bearing bore for pivotably seating the latch.
Conventionally used latch needles, such as disclosed in U.S. Pat. No. 3,934,109 and GB 836,297, typically comprise a needle shank, and a needle latch having a latch shank and a bearing bore. The needle latch is pivotably located in a longitudinal latch slot located within the needle shank, with the bearing bore being pivotably seated on two axle journals that have been pressed out of the needle shank cheeks. This form of seating is advantageous because the construction of the axle journals and the assembly of the needle shank onto the axle journals can be effected in one work cycle. Thus, the manufacture of such latch needles is very economical, and high output rates may be achieved.
Also known are latch needles having latch seatings which are significantly more precise and more wear-resistant than latch needles having pressed-out axle journals, such as disclosed in DE-AS 1 906 892 and DE 3 800 802. Use of this type of latch needle is increasing, particularly when a high-output needle is necessary, such as required for rapidly-running circular knitting machines. These latch needles have a needle shank seated on a throughgoing axial pin that has a smooth, cylindrical jacket surface. The axial pin, which can comprise two pin sections, is inserted into corresponding receiving bores in the shank cheeks. The axial pin is fixed inside the receiving bores by, for example, laser welding or stamp-molding so as to captively fix the pin against relative rotation.
It is also known from DE-AS 1 906 892 to connect the axial pin with the latch shank so as to fix these two parts against relative rotation, and to rotatably seat the ends of the axial pin within corresponding receiving bores in the shank cheeks. The axial pin includes an annular groove, and the latch shank has a corresponding annular ring located in a latch bearing bore for connecting the axial pin and the latch shank together.
For any latch needle, the needle latch must move easily in the longitudinal latch slot of the needle shank, i.e., the pivoting movement of the latch needle about the pressed axle journal or axial pin should generate as little friction as possible so that the movement is essentially unimpeded. To reduce the friction, a particular amount of lateral play is necessary between the adjacent shank cheeks and the base of the latch shank, which is positioned in the longitudinal slot and parallel to the shank cheeks. Thus, gaps are formed between the sides of the longitudinal slot and the adjacent shank cheeks.
During operation of the knitting machine, dust and fluff that detach from the processed yarn cannot be prevented from depositing on parts of the machines and the needles, and in particular, from entering the longitudinal slot. To prevent clogging of the longitudinal slot, the bottom of the slot, i.e., on the back of the needle shank, is typically provided with a through hole which allows the fluff to pass through. However, because the axle journals or axial pin lie exposed in the gap between the latch shank and shank cheeks, particularly finer impurities invariably deposit on these exposed portions. Thus, the impurities may mix with the lubricant provided for lubricating the latch bearing and may, over time, penetrate into the bearing bore of the latch shank. This results in an increased sluggishness and stiffness of the latch bearing, leading to corresponding heat build-up and increased wear, and ultimately to an undesired shortening of the service life of the latch needle. Further, as practical experience has shown, microfissures may also form over time in the region of the bearing bore, which may result in a premature breakage of the latch in the region of the latch bearing.